JULIE ROSE, BYLINE: Several weeks ago, my mom came bounding out of her study yelling come on in here, I've been telling everybody. She'd been entering the first few generations of her family tree on the free website Familysearch.org, when she suddenly linked into a common ancestral line someone else had entered. And it just kept going.

JULIE'S MOM: Oh, my gosh, look at this. Let's do this king guy here. Alfred the Great, king of England 849-899...

ROSE: We click past Odin and a bunch of Trojan kings.

JULIE'S MOM: Oh, there we go - Judah.

ROSE: Now we're into those so-and-so begat so-and-so genealogies in the Bible that take us straight back to Adam, born in the garden of Eden, according to our family tree. Mom was so thrilled she was ready to print the whole thing out and get it framed.

JULIE'S MOM: Until you burst my bubble.

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ROSE: Yeah, sorry Mom.

WARREN BITTNER: It's fiction. It's wishful thinking.

ROSE: Most professional researchers, like Warren Bittner of the Board for Certification of Genealogists, say these family trees dating back to Adam can't be proven. Bittner was at a genealogy conference in Salt Lake City recently, where I also met Rhonda McClure of the New England Historic Genealogical Society. She says records to substantiate a person's identity and lineage are scarce before the 1500s. And last names weren't even common until the 1200s. Royal families are an exception, but McClure says those can be iffy, too.

RHONDA MCCLURE: Even the royals are known to have adjusted accordingly, on occasion, to make their pedigree look a little better when they're trying to farm out the daughter or the son to make a good merge. So you have to use all of that early stuff with a grain of salt.

ROSE: Bogus family trees are nothing new, but websites that let people merge their ancestral lines with a single click have given them new life. And keep in mind, none of these sites police the validity of the family trees people can now create and spread so easily online. Just a decade ago, doing family history took serious commitment, traveling to different archives and writing away for documents. And this...

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ROSE: Long-time genealogy buffs will recognize the sound of microfilm rattling off a projector. Darkened rows of these machines sit vacant now in the five-story Family History Library in Salt Lake City. It's operated by the Church of Jesus Christ of Latter-day Saints, which encourages its members to perform religious rituals for their ancestors. The church has spent a century photographing and archiving global genealogical records. The task now is to digitize them.

DENNIS BRIMHALL: Every single day we add 1.1 million names to the searchable database.

ROSE: Dennis Brimhall is CEO of FamilySearch.org. That's the free website sponsored by the Church of Jesus Christ of Latter-day Saints, where people can collaborate on their genealogy. Through new partnerships with other leading family history sites, the church hopes to have its vast collection of microfilm searchable online within 30 years.

The Web has opened family history to the casually curious, says Ancestry.com CEO Tim Sullivan.

TIM SULLIVAN: More and more people are approaching it in the same way they would spend time on Pinterest or Facebook. It's something to do occasionally. And we like to use the term that there are more people snacking.

ROSE: So sites like Ancestry, which has more than two-million paying subscribers, are launching mobile apps and addictive features that alert you when something new pops up in your family tree. It worked on Roberta Knutson and Sandy Bastian of Moab, Utah.

ROBERTA KNUTSON: So wonderful. You want to check it almost every day because more people are adding to it and you find out. You see pictures of your ancestors that you've never seen before and you log on and you go ooh, my gosh, you know, look at that that's been added. Yeah, the bug will get you.

ROSE: And as the bug spreads, we'll probably be seeing a lot more people linking into phony family trees and boasting of their lineage back to Adam.